Phorophyte preference of an epiphytic orchid (Dendrobium wangliangii) is independent of orchid mycorrhizal fungi that promote seed germination

Epiphytism is an example of an obligate interspecific interaction between plants, where a plant species grows on another plant species for physical support. In epiphytic orchids that rely on suitable host tree species (phorophytes) and mycorrhizal fungi for germination and growth, a distinct preference has been observed for particular host tree species. However, the factors driving this host preference remain unclear. In this study, we investigated whether mycorrhizal fungi that promote seedling development determine the preference of phorophytes in the epiphytic orchid Dendrobium wangliangii. First, we identified the preferred host tree species for this orchid. Next, in vitro and in situ germination experiments were conducted to identify potential fungi that promote seed germination. Finally, high‐throughput sequencing was used to assess the distribution of these fungi on both colonized host trees and potential host trees, including individual trees of the host species not yet colonized by the orchid and trees of another species growing in the vicinity of a colonized tree. Dendrobium wangliangii exhibited a preference for trees within the Fagaceae family. Two Fusarium species from the bark of host trees were identified as the primary fungi that promote seed germination. Successful protocorm formation and seedling development were observed exclusively on preferred phorophytes. Fungal community analyses further indicated that both Fusarium spp. occurred on all potential host trees, suggesting that the host preference of this epiphytic orchid is not constrained by the distribution of suitable mycorrhizal fungi. Synthesis: Regarding the epiphytes that depend on mycorrhizal fungi for successful seedling recruitment, we conclude that strong epiphyte–phorophyte associations do not arise from the limited distribution of mycorrhizal fungi but are more likely the result of other factors inherent in the phorophyte environment. 摘要 在自然界，一种植物生长于另一种植物之上以获得机械支撑，称之为附生，是植物存在专一性种间互作的典型案列。附生兰科植物依赖菌根真菌在合适的附生宿主上实现萌发，现有研究发现附生兰科植物存在对特定附生树种的明显偏好。然而，宿主偏好性形成的机制尚不清楚。 以附生兰科植物金沙江石斛为研究对象，本研究调查了促进幼苗形成的菌根真菌是否决定了的改植物的宿主偏好性。首先，我们鉴定了金沙江石斛偏好性的树木种类。接下来，结合迁地及原生境萌发实验，鉴定到促进金沙江石斛种子萌发的促萌发真菌。最后，利用高通量测序技术评估了促萌发真菌在金沙江石斛生长群落中不同乔木个体树皮中的分布情况，包括被金沙江石斛附生的偏好性宿主个体，未被金沙江石斛定殖的偏好性宿主个体，以及从未被金沙江石斛定殖的非偏好性宿主物种的个体。 金沙江石斛偏好附生于壳斗科植物，从附生宿主植物树皮中鉴定出2种Fusarium属促萌发真菌。原生境共萌发试验表明，仅在金沙江石斛偏好的宿主物种上观察到原球茎和幼苗的形成。真菌群落结构分析进一步发现，具促萌发功能的2种Fusarium属真菌在金沙江石斛所生长群落中所有树种的树皮上广泛分布，这表明这一附生兰科植物的宿主偏好性不受促萌发共生真菌分布的限制。 针对依赖真菌才能实现种子萌发的附生植物而言，附生植物